Nanotechnology: A novel technique borrows from screen printing to provide a way to build tiny devices using miniature stencils

THE field of nanotechnology—making widgets just a few billionths of a metre across—has been slow to take off. One reason for the delay is the difficulty of assembling useful devices from such tiny building blocks. Tobias Kraus, of IBM's Research Laboratories in Zurich, Switzerland, and his colleagues have come up with a new way to print such structures which could help. It is based on screen printing, which uses a stencil and paint to create an image. Existing ways of printing devices at the nanoscale tend to be complex and expensive, and more appropriate for making silicon chips. By contrast, the new technique is easy and cheap.

The researchers first made a patterned template containing holes that were just tens of nanometres deep. They then coated the template with ink made of flecks of gold just 60 nanometres in diameter suspended in an aqueous solution. The ink was kept deliberately thin and exposed to air at a precisely controlled temperature, which concentrated the gold particles at the curved upper surface of the fluid. As the liquid evaporated, the ink became richer in gold, the fluid flowed over the holes, and a single nanoparticle of gold dropped into each one.

The second stage was to transfer the gold from the stencil to a screen, or substrate, by pressing the template onto it. For this transfer to take place successfully, the materials have to be chosen so that the ink is more attracted to the substrate than it is to the stencil. If so, individual nanoparticles of ink will be precisely dotted over the solid surface.

The researchers used their technique to create an image of the sun inspired by the drawings of Robert Fludd, a 17th-century alchemist (the sun is the alchemists' symbol for gold). They used 20,000 particles of gold, each measuring just 60 nanometres across. Dr Kraus thinks their technique could be used to print biosensitive nanoparticles (which are often produced as liquids) onto solid surfaces to make biosensors for use in medical tests. The work was described in the September 2nd issue of Nature Nanotechnology.

Although Dr Kraus has yet to match the accomplishments of his colleague Don Eigler, who used a scanning-tunnelling microscope to manipulate 35 xenon atoms to spell out “IBM” in 1989, his technique may ultimately prove more useful. Despite being just 60 nanometres across, each of his dots contains millions of atoms of gold. At such small scales, the behaviour of particles varies greatly according to their size. It may well be that a bigger blob has more useful properties than a smaller one. Ironically, at the nanoscale, bigger may prove to be better.